1. Field of the Invention
The present invention relates to a spherical bearing for a lock gate door of a lock gate for opening and closing a waterway in a river, canal, or the like, and a lock gate door having the same.
2. Description of the Related Art
A lock gate door for opening and closing a waterway by rotating about a supporting shaft is proposed in, for example, JP-A-2002-285533 (patent document 1). Such a lock gate door is of a non-powered type, and is adapted to exert a moment on a door body in a waterway closing direction due to its own weight, the door body being provided in such a manner as that a shaft is inclined toward the upstream side of the waterway with respect to a vertical axis.
Such a non-powered type lock gate door is adapted to regulate the degree of opening and closing in correspondence with the relative magnitude of water pressure to which the door body is subjected, it is desirable to open and close the door body smoothly and accurately. In addition, since a large load is applied to the supporting shaft of the door body which is subjected to the water pressure, it is difficult to maintain the smooth and accurate opening and closing operation of the door body for a long period of time. It should be noted that the maintenance of the smooth and accurate opening and closing operation of the door body for a long period of time is particularly desirable for the above-described non-powered type lock gate door, but is also desirable for a powered type lock gate door having a power source for opening and closing the door body.